The effect of caffeine, nitrazepam and cigarette smoking on the contingent negative variation in man

Abstract

The effects of caffeine, nitrazepam and cigarette smoking on the contingent negative variation (CNV) in man were studied. In 13 subjects who took caffeine citrate (300 mg), the mean magnitude of the CNV was significantly increased 35–42 min after taking the drug; in 12 subjects who took nitrazepam (2.5 mg), the mean magnitude of the CNV was significantly decreased 35–42 min after drug administration. In 22 smokers, significant changes in CNV magnitude were also observed after smoking one cigarette. However, the direction of change in CNV size following smoking differed in different smokers beyond the variation expected by chance. Some smokers showed consistent increases and others consistent decreases in CNV magnitude immediately after smoking. These changes were interpreted as reflecting stimulant and depressant effects. Correlations of the percentage change in CNV magnitude with rate of nicotine intake and with degree of extraversion suggested that the rate of nicotine intake in extraverted smokers was slower and associated with a stimulant effect while in introverted smokers the rate was faster and associated with a depressant effect in terms of changes in CNV magnitude. There was a significant negative correlation in the smokers between reaction time and CNV magnitude. The amplitude of the N 1-P 2 component of the visual evoked response (VER) was increased after caffeine and decreased after nitrazepam but showed no consistent changes after cigarette smoking and there was no significant overall correlation between VER amplitude and CNV magnitude.